A power metal oxide semiconductor field effect transistor (MOSFET) of a vertical electrode configuration is embedded in a switching power supply having a great current and a high breakdown voltage. In addition, in this kind of element, an intended use as a switching element of a mobile communication equipment, which is a note type personal computer for example, is rapidly increased. In the mobile communication equipment or the like, a synchronous rectifying circuit represented by an AC-DC converter, and a DC-DC converter are embedded.
In order to use as the switching element of the mobile communication equipment or the like, it is desirable that this kind of element saves energy. In order to realize the energy saving, it is one means that this kind of element is set to lower on resistance.
For example, in a method of achieving the low on resistance, a method of setting a field plate electrode below a gate electrode has been paid attention. By setting the field plate electrode below the gate electrode, a depletion of a drift layer is promoted, and it is possible to increase a concentration of impurities in the drift layer. Accordingly, the low on resistance of this kind of element is realized. Further, in order to make this kind of element come to a further energy saving, a low switching loss is demanded in addition to the low on resistance.